To comply with industry regulations, scrubbers are typically installed in urea plants to capture and reduce ammonia and urea dust particles that can be present in exhaust gases from the granulator stack. Usually, scrubbers are vertically-disposed vessels with chimney tray stages and/or mist eliminators. Recirculated urea solution enters at the top of the dust removal section and flows down by gravity while the off-gas enters at the bottom of the scrubber and flows upwards in a countercurrent direction. On its way down, the liquid flows horizontally over the trays or mist eliminators and comes into contact with the off-gas rising through the tray openings, capturing its content of urea dust. Another kind of scrubber utilizes sulfuric acid to capture the NH3 in the off-gas as the respective ammonium salt (AS).
With these conventional scrubbers, however, there is a chance for seepage of sulfate back upstream into other sections of the urea plant, such as the urea granulator or urea synthesis sections. Excess sulfate seepage upstream can lead to corrosion damage to plant parts and can also result in the manufacture of product that is out of desired specification. As such, it is necessary to monitor the slippage of sulfate to the different urea plant sections. Current methods are unable to detect sulfate concentrations present in urea samples at levels of 1 ppm and below. Moreover, the samples that are tested are complicated samples with relatively high concentration of urea, ammonia (NH3), and carbon dioxide (CO2). Thus, there remains a need for improved methods for detecting and measuring sulfate concentrations that are capable of determining sulfate concentrations present in an amount less than 1 ppm, while also being capable of detecting and determining sulfate content in complicated samples with high concentration of urea, ammonia, and carbon dioxide.